1. Field of the Invention
The present invention relates to a semiconductor device equipped with a function for inspecting the native semiconductor integrated-circuit unit and also relates to a method for discriminating bad semiconductor devices from good ones.
2. Description of Related Art
In the conventional step of inspecting semiconductor integrated circuits, which are referred to hereafter simply as ICs, the following methods are adopted for discriminating bad products from good ones in accordance with results produced by the step of examination.
According to a first method, a predetermined array of IC chips made on the surface of a semiconductor wafer are measured by means of a prober or the like. Then, the surfaces of bad IC chips are coated with ink or the like. In a later step, bad products are discriminated from good ones in accordance with whether or not ink exists on the surfaces of the IC chips.
According to a second method, a predetermined array of IC chips made on the surface of a semiconductor wafer are measured by means of a prober or the like. Then, information on each IC chip indicating whether the IC chip is good or bad is recorded in communication media such as a floppy or hard disk. In a later step, only good IC chips are extracted for assembly in accordance with the good/bad information.
An example of a third method is disclosed in Japanese Patent Laid-open No. Heil-21936. According to the third method, a thermally sensitive resin layer is formed on the surface of the semiconductor wafer. Then, the color of the surface of an IC chip, which is determined to be bad with the state of the semiconductor wafer kept as it is, is changed by a special heat generating apparatus external to the wafer. In a later step, bad products are discriminated from good ones in accordance with whether or not the surfaces of the IC chips have changed.
In the case of the first method, however, an ink mark or the like may stick to an adjacent good IC chip. In this case, the good chip will be regarded as a bad one by mistake. In addition, in the case of a semiconductor device such as the charge coupled device (CCD) and a linear sensor, for example, infinitesimal ink dust may be scattered and sticks to the surface of an adjacent IC chip. The dust is then detected at a measurement after the assembly step in which case the assembled product is regarded as a bad one.
In the case of the second method, an error may be generated in the relation associating IC chips with the good/bad information stored in the communication media. In this case, the communication media contains a data error and, in an automatic or manual assembly step based on the good/bad information, it is thus feared that a bad device may be mixed with good ones in the assembled products.
In the case of the third method, the special heat generating apparatus for changing the color of the thermally sensitive resin layer is required and it costs money and labor to maintain and operate the special heat generating apparatus.
An example of a method for solving the problems described above is disclosed by the person submitting this patent application in Japanese Patent Laid-open No. Hei6-53292. According to this method, an operation checking circuit unit is provided on the input-output terminal unit of each IC chip. In the case of a bad IC chip, an excessively large voltage is applied to the operation checking circuit unit. The operation checking circuit unit is damaged by the voltage, changing the color of the surface of the IC chip. In a later step, bad products are discriminated from good ones in accordance with whether or not the surfaces of the IC chips have changed.
In the case of the method described above, however, in spite of the fact that the extremely large voltage is applied only to the operation checking circuit unit, thus, having no effect on the native semiconductor integrated-circuit unit, there is a problem that it takes time to destroy the operation checking circuit unit because elements such as transistors constituting the operation checking circuit unit need to be burned.